The present invention relates to methods and apparatuses for absorbing impact from structures, more particularly to such methods and apparatuses which are mented at berthing locations for absorbing impact from marine (vessels.
"Fenders" are bumpers which are utilized at docks, wharves, piers, moorages and anchorages for absorbing kinetic energy of berthing marine vessels. A fender absorbs kinetic energy of the berthing vessel by converting the kinetic energy into potential energy in the fender material system.
Fender systems have been used, or considered for use, wherein the potential energy is realized essentially in at least one of the following forms: deflection of a fender pile; compression of a rubber fender component; deformation of a foam-filled fender; torsion of a fender's cylindrical shaft; pressurization of a pneumatic fender; fluid motion/pressurization of a hydraulic fender.
Foam-filled fenders generally comprise a resilient, closed-cell foam wrapped with an elastomeric skin. The cellular structure of the foam reacts like individual pneumatic fenders by absorbing energy through deformation. The foam-filled fenders have high energy absorbing capabilities with relatively small reaction force and can float with the tide, handling several surface ship types. Since foam-filled fenders are typically large, they can act as a separator and provide a good standoff.
The U.S. Navy is currently utilizing composite materials in the fabrication of foam-filled fenders for berthing ships. The current design of a foam-filled fender for U.S. Naval ships includes a cylinder having a urethane foam core, overwraps of nylon, and a urethane sprayed over the cylindrical surface. The U.S. Navy's foam-filled fender system has demonstrated effectiveness in terms of reacting certain kinds of ship loads against piers, but has yet to be engineered for generic applications.
The U.S. Naval fenders currently in use are fabricated for a particular class of ship. U.S. Naval vessels which are characterized by different displacements require different fenders to be employed; one reason for this has been the U.S. Navy's need to ensure that a particular U.S. Naval ship's hull loading is maintained below a specific level. Furthermore, fenders of current U.S. Naval design are fixed in terms of the amount of energy which can be reacted. In order to absorb more energy, more or larger current U.S. Naval fenders are required.
Although the U.S. Navy's current foam-filled fender design has been successful in certain modes of practice, it does not lend itself to an analytical design methodology using current design tools. The method for fabricating the U.S. Navy's current foam-filled fender includes wrapping a urethane foam core with nylon fiber, and spraying urethane onto the fiber as it is wound onto the urethane core material; this technique results in operator-to-operator variance in urethane coating thickness or fiber volume fraction.
Accordingly, the mechanism of energy absorption cannot be accurately modeled for current U.S. Navy foam-filled fender systems. The efficacy of a given U.S. Navy foam-filled fender for a particular application requires independent empirical verification. Due to this incapability of advance fender design, the U.S. Navy's current foam-filled fender system necessarily lacks the versatility to predictably adapt to various configurations of marine vessel and/or berth.
Current U.S. Navy fenders are experiencing significant design overloads and are being replaced at an annual cost of millions of dollars per year. Moreover, many pier structures owned by the U.S. Navy and other entities are decrepit or dilapidated. Aging or deteriorating pier structures require renewed analysis to account for degrading mechanical properties. If analytical procedures are not soon established, existing pier structures may be prematurely replaced.